This invention relates to die assemblies for extruding liquids and more particularly to a die assembly which is suitable for extruding high viscosity liquids such as magnetic inks onto a moving substrate.
The conventional prior art practice for applying magnetic inks to a flexible substrate for the manufacture of magnetic recording tapes and the like, has been by the gravure coating technique. In the gravure coating technique a pair of rolls are rotated relative to each other and the substrate on which the coating is to be applied is passed therebetween. One of the rolls is rotated in contact with a supply of the coating material and the rotating roll applies this coating material to one side of the substrate as it is passing thereby.
The gravure technique has several disadvantages. First, coating thickness cannot be changed significantly without changing gravure rolls. Further, there has to be a recirculation of the coating material due to the excessive amount of coating applied over and above what is necessary during the coating process. Moreover, the machinery requires constant operator adjustment, and even then precise thickness control of the coating is not always achieved.
Thus, while the gravure process is an acceptable process for coating high viscosity magnetic inks onto flexible substrates, nevertheless there are certain limitations which adversely affect this gravure technique.
The present invention overcomes many of these defects in that it provides a device which will allow a much closer control of thickness without any equipment change and eliminates the need for any recirculation of ink, reduces the amount of adjustment needed in coating and allows for substantially higher coating speeds in the coating process.